The present invention relates to a protected base useful for making printed circuits and to a method, in a process for making a printed circuit, of forming a base for a printed circuit. More particularly, the present invention relates to the manufacture of a base material for printed circuits, which base material includes a carrier material and a decomposable surface film on the carrier material, and to the applying of the surface film on the carrier material in preparation for the forming of a printed circuit according to the additive technique of making such circuits.
It is already known to produce a base material by bonding resin-impregnated plies together under pressure, then to roughen the surface of the resulting layered press-material, and finally to apply an adhesive film. The application of the adhesive film can also be done on a carrier material, which is not a laminated press material. For example, polytetrafluoroethylene and polyphenylene oxide have been used as the carrier material.
The applying of the adhesive film can be carried out by immersion, or by pouring out a coating onto the carrier. It is usually done on small platforms of carrier material which have been previously cut to size for the intended printed circuit.
The settling of dirt onto the resulting adhesive surface has been avoided only by taking special care to place the finished article in dust-free surroundings. Dust that does get onto the surface of the adhesive can cause flaws in the printed circuit end-product.
In the case where the adhesive film has been applied by the pouring of a coating, it has been the practice to coat first the top or bottom side of the carrier material, then to dry, and then to repeat the process for the remaining side. This causes differences in hardness on the top and bottom sides, because the side which has been coated first undergoes two drying treatments.